Control of glucose metabolism by PACAP : stimulation of insulin secretion and potentiation of insulin action

我们研究了垂体腺苷酸环化酶激活多肽（PACAP）是否作为葡萄糖诱导的胰岛素分泌的胰岛内调节剂。高糖刺激的胰岛素释放可被PACAP特异性抗血清减弱，而非免疫血清则不能。高糖胰岛培养液具有增加β细胞胞质Ca^<2+>浓度（[Ca^<2+>]_i）的能力，该能力被PACAP抗血清中和。PACAP抗血清也能中和合成PACAP的[Ca^<2+>]_i升高作用，但不能中和VIP和胰高血糖素。在胰岛和β细胞系MIN6中，采用逆转录聚合酶链反应（RT-PCR）检测PACAP mRNA的表达，采用代谢标记和免疫印迹法检测PACAP的生物合成。在胰岛中观察pacap选择性受体（PAC1-R）的免疫反应性。[Ca^<2+>]_i测量结合胰岛素抗血清免疫细胞化学表明，PACAP招募更多的无反应的β细胞参与[Ca^<2+>]_i反应。这些结果表明，PACAP是一种新的胰岛物质，由胰岛细胞合成和释放，然后以自分泌/旁分泌的方式，增强和激发β细胞对葡萄糖的反应，从而放大葡萄糖诱导的胰岛胰岛素分泌。接下来，我们探讨了PACAP可能的胰腺外作用。PAC1-R在大鼠脂肪组织和脂肪细胞系3T3-Li中表达。PACAP显著增强333-Li脂肪细胞对胰岛素诱导的2-脱氧葡萄糖的摄取。胰岛素受体β亚基和胰岛素受体底物-1 （IRS-1）均被胰岛素酪氨酸磷酸化，PACAP对其无额外作用。相比之下，胰岛素刺激的磷脂酰肌醇（PI） 3-激酶活性通过PACAP进一步升高。基础2-脱氧葡萄糖摄取和PI 3-激酶活性未受PACAP影响。这些结果表明，PACAP通过增加PI 3-激酶活性来促进胰岛素诱导的葡萄糖摄取，并揭示PACAP不仅增强了胰岛中葡萄糖诱导的胰岛素分泌，还增强了脂肪细胞中的胰岛素作用。少

We examined whether pituitary adenylate cyclase-activating polypeptide (PACAP) serves as an intra-islet regulator of glucose-induced insulin secretion. High glucose-stimulated insulin release from isolated rat islets was attenuated by an antiserum specific for PACAP, but not by nonimmune sera. The islet incubation medium with high glucose possessed a capacity, which was neutralized by the PACAP antiserum, to increase cytosotic Ca^<2+> concentration ([Ca^<2+>]_i) in beta-cells. PACAP antiserum also neutralized the [Ca^<2+>]_i-increasing action of synthetic PACAP, but not VIP and glucagon. In islets and a beta-cell line, MIN6, expression of PACAP mRNA was detected by reverse-transcription polymerase chain reaction (RT-PCR) and biosynthesis of PACAP was detected by metabolic labeling and immunoblotting. Immunoreactivity for PACAP-selective receptor (PAC1-R) was observed in islets. [Ca^<2+>]_i measurements combined with immunocytochemistry with insulin antiserum demonstrated that glucose-u … More nresponsive beta-cells are recruited by PACAP into [Ca^<2+>]_i responses. These results reveal that PACAP is a novel islet substance, which is synthesized and released by islet cells and then) in an autocrine/paracrine manner, potentiates and arouses beta-cell responses to glucose, thereby amplifying glucose-induced insulin secretion in islets.Next, we explored a possible extra-pancreatic action of PACAP.PAC1-R was expressed in the rat fat tissue and an adipocyte cell line, 3T3-Li. PACAP significantly enhanced the insulin-induced 2-deoxyglucose uptake by 333-Li adipocytes. Both insulin receptor beta-subunit and insulin receptor substrate-1 (IRS-1) were tyrosine-phosphorylated by insulin, on which PACAP had no additional effect. In contrast, the insulin-stimulated phosphatidylinositol (PI) 3-kinase activity was further increased by PACAP.The basal 2-deoxyglucose uptake and PI 3-kinase activity were not altered by PACAP.These results indicate that PACAP promotes insulin-induced glucose uptake by increasing PI 3-kinase activity, and reveal that PACAP not only potentiates glucose-induced insulin secretion in islets but also potentiates insulin action in adipocytes. Less